Project Summary: Dr. Michael Shiloh is an infectious disease physician with a well-defined interest in host-pathogen interactions that was fostered as a member of the Tri-lnstitutional medical scientist training program in New York City. His overall career objective is to combine his clinical and basic science interests by studying the underlying mechanisms of M. tuberculosis latency in an academic medical center. This application is constructed to provide a framework to achieve this goal. Through a series of specific aims, Dr. Shiloh will test several hypotheses regarding the role of carbon monoxide (CO) in M. tuberculosis pathogenesis. Specifically, he will test the hypothesis that CO produced by infected macrophages alters the metabolism and gene expression pattern of M. tuberculosis. This will be accomplished using in vitro cellular assays in addition to microarrays from M. tuberculosis exposed to CO in vitro and in vivo. To test the hypothesis that M. tuberculosis utilizes CO for growth in vivo, mutants in the M. tuberculosis CO uptake genes will be tested for their ability to grow on CO in vitro, inside macrophages and inside infected mice. Finally, to test the hypothesis that M. tuberculosis resists the toxic effects of CO, a library of mutants will be exposed to CO and those mutants that fail to survive in the presence of CO will be characterized further. The proposed work is relevant to determining how M. tuberculosis is able to both establish and maintain a dormant infection within the lung. Additionally, this application is designed to complement Dr. Shiloh's prior laboratory experience and provide him with the requisite technical and intellectual background in microbial pathogenesis to function as an independent investigator. A committee of physicians and scientists will oversee Dr. Shiloh's progression towards independence;his scientific development will also be enriched through attendance at several seminar series at UCSF, courses, department retreats and national meetings. UCSF is committed to the development of careers in academic medicine, and at the end of the grant period, Dr. Shiloh will be prepared to embark on a career as an independent physician scientist investigating microbial mechanisms for surviving within the infected host. Relevance: The proposed work is relevant to determining how M. tuberculosis is able to both establish and maintain a latent infection within the lung. Since roughly a third of the world's population harbors a latent infection with M. tuberculosis, understanding the mechanisms involved in latency is vital to developing new ways to prevent, treat and eradicate tuberculosis.